I suspect over-watering ... over-watering yellows the plants, and slows growth ... with a seedling that young and small, it shouldn't have to get any water except maybe every 3rd-4th day ... try letting them dry, until they start to droop slightly .. then, water thoroughly, go thru wet/dry cycles ... ( I have bad habit of over-watering, and that's how my seedlings usually look, lol ) good luck ...